Photoluminescence and micro-Raman scattering in Mn-doped ZnS nanocrystalline semiconductors

Using photoluminescence and Raman scattering, we have studied the optical properties of Mn-doped ZnS nanocrystallites prepared by a microemulsion-hydrothermal method. The PL spectrum shows two distinct peaks in the blue-green region. The PL peak from the nanoparticles, in the region 400–480 nm (3.1–2.6 eV), shifts toward the lower energy with decreasing excitation intensity, which shows that the luminescence originates from the donor–acceptor pair recombination. Such self-activated luminescence could involve the Zn vacancies and Mn acceptors. Micro-Raman scattering measurements on these nanostructured ZnS:Mn crystallites show a low-frequency wing at 315 cm−1 besides the characteristic first-order longitudinal optical phonon at 349 cm−1. The transverse optical phonon from these nanocrystallites at 269 cm−1 along with a much weaker vibrational mode near 220 cm−1 was also observed.